What is problem in vostro 3450

Hello jasinthapa;

Have you made any major changes to your Vostro 3450 recently?
Have you tried a System Restore to an earlier date?

To enable the Biometric scanner, firstly it need to be enabled in the BIOS. Secondly, you will need to install the software that came with the Vostro to be able to recognize the fingerprint/s...
After all that you can configure the extra security features for the rig.
Just go thru the user manual for further technical assistance it is all specified there.

http://www.dell.com/support/drivers/us/en/19

Use drop down lists and choose security sensor